A typical thin film transistor (TFT) is made of a substrate, a gate electrode, an insulation layer, a drain electrode, a source electrode, and a semiconducting layer. The thin film transistor performs a switching operation by modulating an amount of carriers accumulated in an interface between the insulation layer and the semiconductor layer from an accumulation state to a depletion state, with applied voltage to the gate electrode, to change an amount of the current passing between the drain electrode and the source electrode.
State of interface between the insulation layer and the semiconductor layer has a great effect to the property of thin film transistor. For example, water molecule, hydroxyl free radical, and oxygen free radical existing between the insulation layer and the semiconductor layer will affect the state of interface, reducing on/off ratio of current and electron mobility, thereby destroying the stability of thin film transistor.
What is needed, therefore, is a thin film transistor that can overcome the above-described shortcomings.